For higher performance of a semiconductor integrated circuit, it is necessary to increase the performance of a metal insulator semiconductor field effect transistor (MISFET) as a component of the circuit. The device performance has been improved by scaling down of the device. As the channel length of a MISFET is reduced by scaling, the resistance of a channel decreases. Therefore, the device performance is largely influenced by the resistance in the portion other than the channel, that is, the resistance in a source-drain electrode, so-called parasitic resistance. To realize further scaling of the device, it is necessary to reduce the parasitic resistance.
For example, in a MISFET formed on silicon (hereinbelow, also written as Si), about the half of components of the parasitic resistance result from contact resistance in a interface of silicon as the material of a substrate and a metal of the source-drain electrode. Therefore, to reduce the parasitic resistance, it is effective to reduce the contact resistance. A so-called Schottky barrier occurs at the interface between the metal of the electrode and the semiconductor such as silicon, and it causes the contact resistance. There are two approaches to reduce the contact resistance.
The first approach is to increase impurity concentration around the interface on the silicon side. By increasing the impurity concentration, the width of a depletion layer is reduced, the Schottky barrier is thinned, and an effective Schottky barrier height is reduced by an induced mirror effect. However, in theory, activated impurity concentration cannot be increased to the solid solubility limit or higher. Further, the density of impurity which can be activated in reality is below the solid solubility limit, and it is considered that the method is limited.
The second approach is to use, as a metal material of the electrode, a material whose Schottky barrier height a carrier that carries current is low. The Schottky barrier for an electron between nickel monosilicide (hereinbelow, written as NiSi) as a widely used electrode materials and an Si interface has a relatively high value like 0.65 eV. In the case of adding platinum (hereinbelow, also written as Pt) to increase the heat resistance of NiSi, the Schottky barrier for an electron becomes higher. On the other hand, when the electrode metal material is replaced with a rare-earth metal silicide such as erbium (hereinbelow, also written as Er), the Schottky barrier for an electron is lowered to about 0.3 eV. According to the theory of a general Schottky barrier, current flowing in the Schottky barrier changes exponentially with the Schottky barrier height. Consequently, by lowering the Schottky barrier height, the contact resistance between the electrode and the semiconductor is largely improved.
From the viewpoint of the second approach, the metal silicide material replacing NiSi is being studied at present. In particular, with respect to an n-type MISFET, attention is being paid to a rare-earth metal silicide whose Schottky barrier height for an electron is low. However, in the case of using a rare-earth metal silicide for an electrode, interface morphology with silicon degrades considerably. Serious problems such as increase in parasitic resistance and junction leak and variations in the device performance occur. From such a viewpoint, for example, as an electrode of an n-type MISFET, preferably, the property of the bulk is low resistance such as NiSi or Pt-added NiSi, and the interface with silicon has a low Schottky barrier for an electron.
JP-A 2005-123626 (KOKAI) discloses a technique of forming an noncontinuous metal cluster having a low Schottky barrier height at the interface between a metal silicide whose resistance is low and a semiconductor substrate using the Kirkendall effect that atoms of elements in an alloy diffuse at speeds different from each other. According to the technique of JP-A 2005-123626 (KOKAI), by optimizing the work function of the metal of the noncontinuous metal clusters at the interface, both reduction in contact resistance and reduction in the resistance of the electrode itself can be realized.
However, in the technique disclosed in JP-A 2005-123626 (KOKAI), due to the manufacturing method using the Kirkendall effect, a structure in which a metal cluster and a metal silicide of the electrode co-exist at the interface has to be employed. It is consequently difficult to enlarge the area of the interface between the metal cluster whose Schottky barrier height is low and the semiconductor substrate. The metal used for the metal cluster is limited to a metal which does not form a silicide. It is therefore difficult to sufficiently lower the Schottky barrier and there is a problem such that it is difficult to sufficiently lower the contact resistance.